The most popular people, like the most people.
Studies have been done on this. A person who has loads of friends tends to be outward looking, more interested/ focused on others rather than themselves and they're the type of people who if you mentioned a name e.g - do you remember Jane? Their first thought would be something positive about them; oh Jane - the lady with the lovely smile/interesting job/funny sense of humour rather than - oh Jane - the lady that cut me up in the car park, the lady that didn't return a smile that day, or even simply - who? etc etc.
They think more positively about other people, even difficult people, even people who most people dislike - they are always actively seeking that one nice thing about them. Their default is to look for positive traits rather than negative traits.
They also tend to be confident, open body language etc they view all other people as interesting.
So say they're at the supermarket and see Susan their first thought is - oh look it's super Susan, wonder how HER dog is now after that operation last year. I must go and say hello to HER. SHE'S such a lovely person. Oh she's just walked past and not noticed me - supermarkets are such busy places and she's probably like me lost in thought......Susan! Hi! It's been ages! It's so good to see you! How are you? How's your lovely dog?
Rather than - oh it's Susan, I wonder if she remembers ME. I wonder if she'll say hello to ME. Maybe I should wave, but she hasn't waved to ME. Maybe she'll think I'M weird or ignore ME if I did. Oh she walked past and ignored ME. She doesn't like ME. No one does. I'm going to go this way and hopefully avoid her now.
That's internal monologue - and the difference between people who make friends easily and those that don't is what's going off inside your own head.
When you think about it and think about the people who make friends effortlessly, the people who everyone seem to like, the ones who seem to just rock up and instantly everyone flocks to them and it all seems so easy for them. This is their key trait. And when you're talking to them, you feel good because they are honing in on all your key positive traits and they focus on all the topics that make you tick and happy - if you're arty - they're asking questions about art. If you're sporty the topic is on sport. If you're bookish you find they've opened a conversation about books. You walk away and you feel good.
For these kind of people - they get pleasure from making people feel good.
These people are rare as most people are focused on themselves, but they do exist.
They just approach people with a genuine caring nature and interest - they aren't looking to gain anything.
And like every personality trait there's a spectrum - people who score really low on this will have less friends. People who score higher will have more. People who score full marks will be super popular. If you can nudge yourself up the spectrum by interrupting your own negative internal dialogue- you can/will make more friends.
Have a look at Vanessa Van Edwards - she has a website the science of people. And she's done Ted talks and lots of podcasts on YouTube. Her whole career is based on the science and psychology of likability.